Everyone of a certain age can remember where they were and what they were doing when they heard about the al-Qaeda attacks on the Pentagon and Pennsylvania and the destruction of the twin towers of the World Trade Center in New York City, reduced to rubble by civilian aircraft turned into weapons of mass destruction. In ambition and scale - and with their thousands of innocent victims - the events of 11 September 2001 were a terrorist attack for an age of globalisation: an age of 24-hour satellite news channels, the internet, mobile phones and the instantly replicable image.
In seeking to murder and terrify so many, al-Qaeda channelled the destructive impulses of American entertainment culture - the disaster movie, the apocalyptic computer game, the hi-tech thriller - and made of a people's uneasy fantasies a terrifying actuality. The hijackers who flew the planes into the towers must have known that they were creating images of catastrophe that would haunt our imaginings and our dreams, that their actions would have profound political and economic consequences, as they did. We were at the beginning of what would become a decade of war, which continues today and will no doubt extend long into the future.
In Mao II, published in 1991, the American novelist Don DeLillo wrote, eccentrically as it was then thought, of how terrorists and bomb-makers had replaced writers and artists as the myth-makers of our age. Their work "involves mid-air explosions and crumbled buildings. This is the new tragic narrative," DeLillo wrote. "Terror makes the new future possible."
Certainly when Osama Bin Laden authorised the attacks of 11 September 2001, which were so patiently and meticulously planned, he knew that he and his suicidal operatives had the means to make the new future possible. What would that future hold for us all?
In the immediate aftermath of the attacks, it felt to many as if we were entering a period of darkness, as the US and its allies, principally the United Kingdom, prepared their response. What is often forgotten all these years later is that there was a sense, too, that this crisis offered an unrivalled opportunity to transform the world for the better, that it was a time of despair but also one of hope and solidarity between peoples. "We are all Americans" was the resonant headline on the front page of Le Monde the morning after the attacks.
In his speech to the Labour party conference in October 2001, Tony Blair captured this mood: "Round the world, 11 September is bringing governments and people to reflect, consider and change . . . There is a coming together. The power of community is asserting itself . . . I have long believed this interdependence defines the new world we live in." He went on: "This is a moment to seize. The kaleidoscope has been shaken. The pieces are in flux. Soon, they will settle again. Before they do, let us reorder the world around us . . . 'By the strength of our common endeavour, we achieve more together than we can alone.'"
The hope did not last. The goodwill that many felt for America and Americans on 11 September 2001 was wasted. The US responded to the attacks by embarking on a series of misconceived and mismanaged wars, first in Afghanistan and then in Iraq, just as Bin Laden would have hoped.
Brown University's Costs of War project estimates that the financial burden to the US of these wars is between $3.2trn and $4trn. So far, 1,752 US service personnel have been killed in Afghanistan and 4,474 in Iraq. The UK has lost 380 soldiers in Afghanistan and 179 in Iraq. The civilian death toll in Iraq has been estimated at anything between 120,000 and one million; the comparable figure in Afghanistan is estimated to be in the tens of thousands. So many lives lost and so many resources squandered - and for what? These sacrifices haven't made us feel any more secure. In an ICD Research poll conducted for the New Statesman, only 13 per cent of Britons said they felt safer today than they did on 10 September 2001.
During these wars, many of our most cherished liberal values were tarnished. Muslims everywhere were demonised and Islamophobia became respectable, even among those who purported to be on the left. The Americans implemented the "extraordinary rendition" of terror suspects and countenanced their torture and imprisonment, without charge, in Guantanamo Bay.
At home, following the London bombings of 7 July 2005, in which 56 people died, the Labour government attempted to raise the maximum period for pre-charge detention to 90 days, as it struggled to contain the dangers posed by young British Muslims radicalised by the wars in Iraq and Afghanistan, and provoked by Saudi-funded Islamist preachers working in mosques.
Above all, the doctrine of liberal intervention, even on so-called humanitarian grounds, was gravely undermined by the misadventures in Iraq and Afghanistan. Mr Blair's dream of a new, interdependent world order turned out to be no more than the delusion of a western triumphalist who believed that history was moving in his direction and that authoritarian states and premodern theocracies could be bombed into embracing democracy, free markets and the rule of law.
As Rory Stewart, the Conservative MP and former deputy governor of the Iraqi province of Maysan, says on page 32: "9/11 turned intervention into war. Western foreign policy since has been driven by fear, pride and guilt. The US and its allies have exaggerated the threat posed by 'failed states'. We have overestimated our power to transform those states . . . Emotions, rather than any rational analysis, trapped us in these deserts."
It could have been so different. The appalling September 2001 attacks did fleetingly create the conditions in which a new world order could have emerged, one founded on the principles of international law, with nations operating not unilaterally but more effectively and transparently through supranational organisations such as the European Union, the African Union and the Arab League. Instead, we had unilateral declarations of war. We had wars fought without any sense of what their ending might be.
The US and the UK no longer speak of victory in Afghanistan, but only of retreat and of striking deals with the hated Taliban, with whom they could have once negotiated from a position of strength rather than weakness. A decade after the attacks of 9/11, western leaders no longer proclaim their desire to reorder the world.
Ravaged by the financial and sovereign debt crises, they are struggling to adjust to decline and to accept the limits of their own reduced power. The kaleidoscope was shaken on that clear, blue September day in New York. The pieces have not yet settled and will never be allowed to settle until the lessons from the misadventures of the past decade have been learned - if they ever will be.